1. Field of the Invention
The invention relates to a seat back frame.
2. Description of Related Art
Japanese Patent Application Publication No. 2008-194289 (JP 2008-194289 A), for example, describes a seat back frame in which a main frame that forms a frame of a seat back of a main seat is integrally formed with an auxiliary frame that forms a frame of a seat back of an auxiliary seat adjacent to the main seat in a width direction. As shown in FIGS. 7, 8A, and 8B, a main frame 120f of a seat back frame 114f in JP 2008-194289 A has a side frame 122 formed on both sides, and an upper frame 124 that connects upper portions of the side frames 122 together. Also, an auxiliary frame 130f is formed by a generally L-shaped tube-shaped member being connected to the main frame 120f, in a position adjacent to the main frame 120f in the width direction. Here, the auxiliary frame 130f has a frame body in which hollow steel pipe has been bent in a generally inverted L-shape. The auxiliary frame 130f has a flat end portion 132 that has been press-formed into a generally flat shape. The flat end portion 132 is welded to a shoulder portion of the upper frame 124 of the main frame 120f. Also, because the end portion (i.e., the flat end portion 132) of the auxiliary frame 130f is press-formed into a flat shape, an auxiliary plate 150 is welded to the flat end portion 132 in order to ensure rigidity of the connecting portion.
However, with the seat back frame 114f described in JP 2008-194289 A, there is room for improvement because the auxiliary plate 150 must be provided on the connecting portion where the auxiliary frame 130f is connected to the main frame 120f, which increases the number of parts. Also, the end portion of the auxiliary frame 130f must be press-formed into the flat end portion 132, so the manufacturing cost may also increase.